FIG. 1 diagrammatically shows a raster of an interlace system. In this Figure the even field scanning line 1 and the odd field scanning line 2 are deviated 1/2.multidot.H (1/2 of a horizontal scanning period) in its phase, and they are inter-located with each other. For example, the even and odd fields are repeatedly displayed at each of 20 msec in a CCIR B/G
system, the screen vibrates at a period of 40 msec and at a frequency of 25 Hz, and the width of the vibration becomes 1/2.multidot.H of vertical direction distance.
Such a vibration occurring in a general television screen presents no trouble, however it is difficult to watch little characters in the character-broadcasting also caused by it being a still picture. In order to solve this problem it is planned to conduct a non-interlacing, that is, a multiplying of the even and odd field scanning lines although the picture element becomes slightly rough. As a general method to conduct such a non-interlacing, it is considered to deviate the timing of the vertical synchronicity 1/2.multidot.H one after another frame.
FIG. 2 shows signal waveforms of a television receiver, wherein FIG. 2(a) shows a signal waveform obtained by viewing the television signal 30 at a timing of horizontal synchronicity. FIG. 2(b) shows a signal waveform obtained by extracting the synchronizing signal 40 from the signal of FIG. 2(a). This includes the vertical and horizontal synchronizing signal. FIG. 2(c) shows a vertical synchronizing signal 20 with the horizontal synchronizing signal being removed by integrating the waveform of FIG. 2(b). This signal becomes a timing signal for the vertical deflection circuit.
In a CCIR B/G PAL system there exist 625 scanning lines in one frame of 40 msec, and the number of scanning lines in one field of 20 msec is 312.5, and two fields constitute one frame. The existence of the 0.5 scanning line among the 312.5 scanning lines necessitates interlacing.
In order to conduct a non-interlacing it is enough to determine the number of scanning lines at each field as 312, 313, 312, 313, . . . . Thus it is possible to obtain a raster of non-interlacing which has substantially no-problem. It is a minor problem that a difference arises in a raster size depending on the difference of the number of the scanning lines at each field.
The scanning period for each field becomes:
20 msec-1/2.multidot.H PA1 20 msec+1/2.multidot.H PA1 20 msec-1/2.multidot.H
where, H is equal to 64 .mu.sec.
FIG. 2(c) shows a timing of a vertical synchronizing signal for obtaining a different scanning period at each field. The waveform 20a of the left side portion of the vertical synchronizing signal 20 is shifted to the left side by 1/2.multidot.H as compared with the normal vertical synchronizing signal 20 at an interval of 40 msec to become a waveform 20a' shown in dotted lines.
However, the vertical synchronizing circuit has a subtle operation, and a sufficient consideration of the wave-formation of the synchronizing signal and the circuit arrangement of the peripheral circuits is required in conducting a normal interlacing. Furthermore, it is required to conduct an exact synchronization in all conditions of television signals such as the condition where the synchronizing signal becomes long or short caused by the noise in a weak electric field or by the transmitter side's cause, and the condition where the synchronizing signal may have a default caused by the sag of the television signal.
Accordingly, it is difficult to advance the phase of the vertical synchronizing signal 1/2.multidot.H by this vertical synchronizing cirucit in television receivers which are produced by mass-production because it is required for the products to have the stability in their performances.